newton/tests/test_equality_constraints.py (1)

170-207: Equality-constraint remapping test logic is sound

The per-world index expectations (3 bodies & 3 joints per robot, 2 constraints per world, constraints ordered as connect then joint) correctly mirror add_builder’s offset behavior and the way equality constraints are appended. The assertions on equality_constraint_body1/2 and equality_constraint_joint1/2 look accurate and should reliably catch future regressions in remapping.

Optionally, you could also assert on model.equality_constraint_world for the same indices to lock in the world assignment semantics, but the current checks are already strong for this PR’s intent.

newton/_src/sim/builder.py (1)

1523-1543: Equality-constraint remapping in add_builder() is consistent with body/joint offsets

Using start_body_idx and start_joint_idx here correctly maps the sub-builder’s constraint body/joint indices into the destination builder’s index space, and the explicit handling of -1 preserves world-sentinel semantics. Moving equality_constraint_* out of more_builder_attrs avoids duplicate, un-remapped copies, so the final arrays stay coherent with the new per-world tests.

If you ever touch this again, you might consider extracting this block into a small helper (e.g., _merge_equality_constraints(...)) for clarity, but functionally this looks solid.

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Learnt from: adenzler-nvidia
Repo: newton-physics/newton PR: 1107
File: newton/_src/solvers/mujoco/kernels.py:973-974
Timestamp: 2025-11-24T08:05:21.390Z
Learning: In Newton's MuJoCo solver integration (newton/_src/solvers/mujoco/), the mapping between Newton joints and MuJoCo joints is not 1-to-1. Instead, each Newton DOF maps to a distinct MuJoCo joint. This means that for multi-DOF joints (like D6 with 6 DOFs), there will be 6 corresponding MuJoCo joints, each with its own properties (margin, solimp, solref, etc.). The mapping is done via dof_to_mjc_joint array, ensuring each DOF's properties are written to its own MuJoCo joint without overwriting.

Learnt from: eric-heiden
Repo: newton-physics/newton PR: 710
File: newton/_src/utils/import_usd.py:597-599
Timestamp: 2025-09-24T00:26:54.486Z
Learning: In the Newton ModelBuilder class, `joint_count`, `body_count`, `articulation_count`, and `shape_count` are implemented as property decorated methods, so they should be accessed as attributes (e.g., `builder.joint_count`) rather than called as methods (e.g., `builder.joint_count()`).